Abstract
Serum luteinizing hormone (LH) concentrations were measured at 4, 6, 8 and 10 mo of age in estradiol-17β (E 2)-treated (n = 4) and contemporary control steers (n = 4). Serum LH was measured in samples collected at 30-min intervals starting at 0600 h for 12 h and for an additional 6 h following luteinizing hormone-releasing hormone (LHRH) injection. Estradiol-17β suppressed mean serum LH concentrations at all ages (P<0.01), but it suppressed pulsatile release of LH only at 4 and 6 mo (P<0.01), not 8 and 10 mo of age. Luteinizing hormone release in response to LHRH, expressed as the area under the secretory curve, was larger and LH concentrations returned to pre-LHRH levels later in E 2-treated steers (P<0.01). Peak LH concentrations after LHRH varied with age (P<0.05) but not E 2 treatment. These results suggest that E 2 suppression of LH in steers occurs at the hypothalamic level and developmental changes take place within the hypothalamicpituitary axis in absence of androgen feedback from the testis.
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